206 



NATURE 



\jfune 30, 1 88 1 



the same as that due to a current of strength m flowing along 

 the short line joiijing the source to the sink. Now the current 

 at any point produced by a source and sink placed clo?e to- 

 gether at a distance ds, is exactly the same as the magnetic force at 

 the same point produced by a magnet joining the source and 

 sinli whose moment is mds, and direction of magnetisation 

 along the line joining the source and tink. Hence if we have 

 any system of currents in the field, and find by the application 

 of the methods given by Sir \V. Thomson in his paper on 

 " Inverse Problems " the di>tribution of magnetism which would 

 produce a magnetic field such that the magnetic force at any 

 point was equal in magnitude and direction to the current at the 

 point, the magnetic action of the system of currents will by the 

 proposition just stated be the same as that due to currents w hose 

 intensity and direction coincide with the intensity and direction 

 of the magnetisation producing the said magnetic field. Thus 

 instead of currents occupying the whole of the medium, we have 

 only to consider currents occupying a limited portion of it. 

 This is, we think, all that can be fandy stated about this point, 

 and it will be seen tliat, to say the least. Prof. Roh land's s ate- 

 ment that "the action in such a medium reduces itself to an 

 action between magnets and electromotive forces instead of 

 between magnets and currents," is not a clear way of putting it. 

 Prof. Rowland in this part of the subject introduces a new term, 

 viz., magneto-motive force; this is a force supposed to exist 

 between two magnetic poles so as to cause the same number of 

 lines of induction to pass betueen the points as to flow out of 

 either of them ; it is proportional to the magneti-ation, and 

 seems only introduced for the sake of making more evident the 

 fact that currents are related to electr. miotive forces like lines of 

 induction to magnetisation, or with the new terminology to 

 magneto motive forces. This was pointed out by Maxwell in 

 his paper on "Faraday's Lines of Force" published in the 

 Cambridge Transactions for 1856. 



The last part of the paper, which is also the most interesting, 

 contains the explanation, by means of the new action discovered 

 hy Mr. Hall, of the magnetic rotation of the plane of polarisa- 

 tion of light. By adding to the old expression of the electro- 

 motive force a term representing the force discovered by Mr. 

 Hall, Prof. Rowland obtains an expression for the rotation of 

 the plane of polarisation of exactly the same form as the one 

 given by Maxwell in § 829 of the "Electricity and Magnetism." 



J. J. Thomson 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — The report of the Botanic Garden Syndicate 

 states that during the past year valuable additions have been 

 made to the collections of ferns and orchids, and many choice 

 stove and greenhouse plants have been received. The collection 

 of hardy, herbaceous, and al| ine plants has been much in- 

 creased, and the rockery furnished with many rare alpine 

 species. The genera Iris, Narcissus, and Helleboms have re- 

 ceived special attention. During the year, 1594 labels have 

 been written in large letters. The curator, Mr. Lynch, has 

 extended the correspondence of the Gardens with botanic gar- 

 dens, nurserymen, and private cultivators : 2600 plants have 

 been received, and 1285 packets of seeds. 



In consequence of the decision of the Duke of Devonshire in 

 favour of the legality of the recent vote of the Senate admitting 

 women to the Previous and the Tripos Examinations, the first 

 lists in which the names of women who have passed the Previous 

 and any Tripos Examination, have appeared in the University 

 Reporter. In the Natural Sciences Tripos, Part I, Class 2, is the 

 name of Miss Anelay of Girton. In the Previous Examination 

 twelve Girton students and two Newnham students have passed 

 in one or more parts of the examination. 



Local Lectures. — In spite of the removal of several im- 

 portant districts trcm the scope of these lectures by the establish- 

 ment of local colleges, the numbers attending lectures during 

 the past winter have been 4369 as against 5009 in the preceding 

 winter ; and the reduction in numbers is due to the absence of 

 the South Wales centre from the lists, the Syndicate having 

 been unable to make adequate arrangements for this district, 

 owing to their engagements elsewhere. South Wales is again 

 to be vigorously worked in the coming session. Dr. R. D. 

 Roberts of Clare College has been appointed Assistant Secretary 

 for the purposes of the local lectures. The courses of lectures 

 on physical science subjects in the past winter have included Mr. 



Teall's on Early Man in Western Europe, and the Origin of 

 Rocks and Scenery of ihe British Isles at Nottingham and 

 Derby, Mr. J. E. Marr's on Geology at Carlisle and Penrith, Mr. 

 E. Carpenter's on the Science and History of Music at Notting- 

 ham, and on Light at Chesterfield, Mr. Cair Robinson on Gases 

 and on Chemistry at Hull, and by Mr. H. N. Read on Botany 

 at the Crystal Palace. 



SCIENTIFIC SERIALS 

 Journal of the Franklin Institute, June. — The flight of birds 



and the mechanical principles involved, by A. C. Campbell. 



Recent advances in photography, negative and positive, by J. 

 Carbutt. 



Journal de Physique, June. — On registering apparatus for 

 atmospheric electricity and terrestrial magneti-m, by M. Mascart. 

 — On radiophony (third memoir), by M. Mercadier. — On the con- 

 traction of galvanic deposits and its relation to Peltier's pheno- 

 menon, by M. Bouty.— Projection of the Li^sajous fiijures with 

 differences of phase variable at will, by M. Crova. — Production 

 of electric currents in any system of fixed conducting wires, by 

 M. Brillouin. 



Reale Istituto Lombardo di Seienze e Lettere. Rendiconti. Vol. 

 xiv. fasc. viii.-ix. — On the question whether American vines may 

 be imported from phyllc.xerised or suspected districts without 

 risk, by Count Trevisan. — Difference of loni:itude between the 

 observatories of Genoa, Milan, Naples, and Padua, by Prof. 

 Celoria. — On the slocking of Italian lakes with fishes, by Prof. 

 Pavesi and Dr. Sulzer. — Toradelphia of a scorpion, by Prof. 

 Pavesi. — Monstrosity of a fresh-water Crustacean (Astacus Jluvi- 

 atilis), by Prof. Maggi. — Cremation and legal medicine, by Dr. 

 Bififi. 



Rivista Scientifico-Industrialc, No. 9, May 15. — Two new 

 applications of the electric light, by Prof. Ferrini. — Mercury 

 air-pump, by S. Serravalle. — New method of qualitative 

 chemical analysis, by L. Mauri. 



Aili delta R. Accademia dei Lined, vol. v. fasc. 12. — Descrip- 

 tion of a terrestrial trom'te which occurred in 1456, by S. 

 Blaserna . 



SOCIETIES AND ACADEMIES 

 London 

 Royal Society,Jane 16. — " On the Reversal of the Lines of 



Metallic Vapours. No. VIII. (Iron, Titanium, Chromium, 

 and Aluminium.)" By Professors Liveing and Dewar. 



In their last communication on this subject the authors ob- 

 served that iron introduced as metal or as chloride into the 

 electric arc in a lime crucible in the way which had proved suc- 

 cessful in the case of many other metals, gave no reversals. 

 They succeeded however in reversing some ten of the brightest 

 lines of iron, mostly in the blue and violet, by passing an iron 

 wire through one of the carbons, so as to keep up a constant 

 supply of iron in the arc. Considering the great number of 

 iron lines, and that so many of them are strongly represented 

 amongst the Fraunhofer lines, it seemed somewhat surprising 

 that it should be difficult to obtain a reversing layer of iron 

 vapour in the arc inclosed in an intensely heated crucible. A 

 like remark might be made respecting titanium, which is almost 

 as well lepresented as iron in the Fraunhofer lines, but has 

 heretofore given no reversals. Almost the same might be said 

 of chromium, except that the number of chromium lines is so 

 much less than than that of either of the other tw o metals. 



They have since found that most, if not all, of the strong lines 

 of these three metals may be reversed by proper management of 

 the atmosphere and supply of metal in the crucible. Indeed 

 with regard to iron the method employed w ith other metals was 

 successful so far as the ultra-violet rays were concerned, though 

 it failed for less refrangible rays. When iron has been put into 

 the crucible through which the arc of a Siemens' dynamo-elec- 

 tric machine is passing, and then fragments of magnesium 

 dropped in from time to time, most of the strong ultra violet 

 lines of iron are reversed. The magnesium seems to supply a 

 highly reducing atmosphere, and to some extent carry with it the 

 iron vapour. It also produces a good deal of continuous spec- 

 trum, at least in certain regions, and against this the iron lines 

 are often depicted on the photographic plates sharply reversed. 

 In this way the authors have observed the reversal of the strong 



